1. Field of the Invention
The present invention relates to a drive circuit for a step motor employing thyristors.
2. Brief Description of the Background of the Invention Including Prior Art
The application of a step motor with a relatively low self holding torque results in the advantage of a correspondingly low energy requirement for performing each step. For avoiding of undesired motions caused by mechanical disturbances such as for example small shocks the self holding torque can be supported by an additional magnetic field, which can be generated from a current flowing in the rest position in a stator winding.
The switching on of the stator windings is performed by way of thyristors connected in series, where the conducting state of the thyristors is maintained in each case by the current flowing through them. In the context of the present invention a thyristor refers generically to thyratronlike solid-state devices such as silicon controlled rectifiers and in particular pnpn-type bistable semiconductor devices having anode, cathode and gate terminals and useable as an electronic switch.
For switching off of a stator winding the corresponding thyristor has to be switched off and in general a special quench device has to be provided for this purpose. It is an advantage, if the switching on step of another stator winding can be employed for at the same time quenching said thyristor to switch off the current flow.